Oh, the joy of using "modern" batteries. Or, as mnem would say, "They don't make them like they used to."
Can you hear the vintage Eveready cells laughing?
Electronix Repair hack #678 (Mostly developed for resurrecting battery-defiled remote controls): Scrub battery connectors and PCBs with a toothbrush (or where possible without destroying plastic, a stainless steel detail brush) and Windex (Real Windex, or the good store brand stuff that you can smell has with lots of ammonia in it) to neutralize alkaline deposits and clean battery contacts down to clean metal. Rinse with distilled water and dry on a towel on your dash in the sun, or use your hair dryer/heat gun on low as conditions demand.
Once battery contacts are clean, smear a little silicone dielectric grease between the batteries and contacts to prevent corrosive relapse common with cleaned battery terminals. This stuff is available at your local Auto Parts Hell for a buck; it's made to go inside spark plug boots/coil packs when you replace the plugs.
mnem
We now return you to your regularly scheduled insanity.